Phosphors are lambertian emitters, emitting light in all directions. In traditional LED implementations, phosphor is applied on the LED chip, in a silicone matrix in proximity to the LED or to the outside of an LED dome or other LED packaging. A dome may be applied to an LED chip coated with phosphor to control the light beam angle (shape) from lambertian to a very narrow spot. Such devices range from hemispherical lenses to T-5 mm (T 1¾) aspheres. One conventional system for producing white light LEDs, for example, is constructed with pump blue/UV LED chips and a proximate mixture of phosphor in a binding matrix such as silicone. The term “goop in a cup” is used to describe LEDs with flat or very nearly flat phosphor and silicone mixture over a blue pump. In remote phosphor systems, phosphor is applied away from the chip on the outside of a dome or inside of a hemispherical shell to increase converting efficiency. However, an additional lens may be needed to control light beam shape. The GE VIO® employs the remote phosphor solution.
Current systems suffer efficiency losses due to heating of the LED chip and the phosphor particles. Additionally, many current system require secondary optics or additional lenses to shape the light emitted from a dome or phosphor coated LED into a desired beam angle. The coupling of a lens to a dome causes efficiency losses of approximately 15%. Furthermore, current systems suffer conversion losses when multiple color phosphors are used due to self absorption. For instance, a red-emitting phosphor may absorb down-converted light from a green-emitting phosphor instead of the pump wavelength, thereby introducing further losses.
The following U.S. Patents describe prior efforts in addressing some of the challenges in phosphor converting light emitting devices. U.S. Pat. No. 6,614,179 discloses a light emitting device with blue light emitting diode and phosphor components. U.S. Pat. Nos. 5,998,925, 6,069,440, and 6,608,332 disclose white light emitting devices, each having a nitride compound semiconductor and a phosphor containing yttrium-aluminum-garnet (YAG) elements. The nitride compound semiconductor is used as a light emitting layer. The phosphor absorbs a part of light emitted by the light emitting layer and emits light of a wavelength different from that of the absorbed light. U.S. Pat. No. 6,737,681 discloses chip placement designs for white light packages. One example includes a fluorescent member having a curved surface or concave arc that extends from the height of the bottom of a case obliquely upward in a shape that continues along substantially the entire circumference of an oval or elongated round shape. It reflects the light emitted from the side faces of a semiconductor light emitting element to more efficiently utilize part of the light emitted from the semiconductor light emitting element and most of the light emitted from the side faces. U.S. Pat. No. 6,924,596 discloses a color conversion type light emitting apparatus having a light emitting device and a color converting member formed from an epoxy resin containing a photoluminescence fluorescent substance and directly coating the light emitting device. U.S. Pat. Nos. 7,091,656 and 7,247,257 disclose light emitting devices that use a mixture of at least two phosphors for more complete color rendering. U.S. Pat. No. 7,071,616 discloses a light source having a blue LED, an optical guide plate having a planar main surface and an edge face receiving injection of the light from the blue LED and a coating material of transparent resin or glass containing fluorescent materials positioned between the blue LED and the optical guide plate. The optical guide plate is used for the final light mixing. U.S. Pat. Nos. 7,026,756, 7,126,274, 7,329,988, 7,362,048 disclose light emitting devices with blue light LED and phosphor components, including the emission spectra and package designs for display backlight. U.S. Pat. No. 6,960,878 discloses an LED chip having a blue die and a phosphor and including an epoxy resin for better reliability and optical stability. U.S. Pat. No. 7,256,468 discloses a light emitting device having a light emitting element and a metal package with a heat radiating characteristic and mechanical strength for housing the light emitting element.